Optical element, method for manufacturing the same, and electronic apparatus

ABSTRACT

An optical element includes a substrate, a plurality of reflective reflection layers on the substrate, and an absorbing layer over the reflection layers. The reflection layers are arranged in a striped manner in plan view. The absorbing layer absorbs polarized light oscillating in the direction in which the reflection layers extend. The optical element also includes an oxide film on the substrate between the reflection layers and on the absorbing layer. The oxide film is formed by oxidizing the absorbing layer.

BACKGROUND

1. Technical Field

The present invention relates to an optical element, a method formanufacturing the same, and an electronic apparatus.

2. Related Art

For example, in a projector that is a type of electronic apparatus,optical elements are disposed at each side of a liquid light valve. Theoptical element may be a wire grid polarization element disclosed inJP-A-2012-98469. The polarization element includes a transparentsubstrate and a metal grid disposed over the substrate in such a mannerthat the ribs or bar members of the grip are arranged with a pitchsmaller than the wavelength of light used.

Since this grid is made of an inorganic material, the polarizationelement is less likely to deteriorate than polarization elements usingan organic material, even if it is irradiated with light, and is thususeful for brighter liquid crystal projectors which are increasingly indemand.

For example, in a process for manufacturing a polarization element, amultilayer composite is formed on a substrate by forming an aluminumlayer, a silicon oxide layer, and a silicon layer in this order on asubstrate, and a resist pattern is formed in a striped manner on thecomposite. The multilayer composite is then etched at one time using theresist pattern as a mask, and is thus formed into a multilayer grid in astriped manner with a large aspect ratio in plan view.

Unfortunately, the grid has a multilayer structure with a large aspectratio and the layers forming the multilayer structure have differentetching rates. Consequently, the amount of etching is varied. If etchingis intended to be performed up to the interface between the lowermostaluminum layer and the substrate, therefore, the etching must beperformed allowing for variation in etching amount. Consequently, theside surfaces of the stripes of the multilayer structure are excessivelyetched, and the width of the stripes is reduced. Thus, it is difficultto form a small and fine polarization element.

SUMMARY

An advantage of some aspects of the invention is that it provides anoptical element, a method for manufacturing the same, and an electronicapparatus as below.

Application 1

According to an aspect of the invention, there is provided an opticalelement including a substrate, a plurality of reflection layers on oneside of the substrate in a striped manner in plan view, and an absorbinglayer on the side of the reflection layers opposite the substrate, andan oxide film covering the absorbing layer and portions between any twoadjacent reflection layers. The oxide film is made of an oxide of amaterial contained in the absorbing layer.

This structure is formed by forming the absorbing layer after formingthe reflection layers. This process can reduce variation in etchingamount resulting from the difference in etching rate between thematerials compared to the case of forming the reflection layers and theabsorbing layer at one time by etching. Accordingly, finely stripedreflection layers can be formed. Consequently, contrast and brightnesscan be improved. Also, the oxide film is made of an oxide formed byoxidizing a material contained in the absorbing layer. This prevents thedecrease in optical transmittance between the reflection layers.

Application 2

Preferably, the substrate has grooves therein between any two adjacentreflection layers, and the oxide film in part lies in the grooves.

This structure is formed by forming the absorbing layer after formingthe reflection layers. This process can reduce variation in etchingamount resulting from the difference in etching rate between thematerials compared to the case of forming the reflection layers and theabsorbing layer at one time by etching. Accordingly, finely stripedreflection layers can be formed. Consequently, contrast and brightnesscan be improved.

Also, the oxide film is formed in the grooves. Consequently, theportions between the reflection layers are nearly transparent, andaccordingly, the optical transmittance between the reflection layersdoes not decrease.

Application 3

Preferably, the optical element further includes a dielectric layerbetween each of the reflection layers and the absorbing layer.

In this structure, the dielectric layer between the reflection layersand the absorbing layer prevents the constituent elements in thereflection layers and the absorbing layers from diffusing mutually.Thus, fluctuation in performance of separating polarized lightcomponents, resulting from diffusion can be reduced.

Application 4

Preferably, the reflection layers contain at least one selected from thegroup consisting of aluminum, silver, copper, chromium, titanium,nickel, tungsten, and iron.

The reflection layers made of such a material allows an oxide film(dielectric layer) to be easily formed by thermal oxidation or the like.

Application 5

Preferably, the absorbing layer contains at least one selected from thegroup consisting of silicon, germanium, and chromium.

The use of such a material achieves an optical element capable ofabsorbing light, that is, having a low reflectance.

Application 6

Preferably, the dielectric layer is made of silicon oxide.

In this instance, the silicon oxide layer can be easily formed bythermal oxidation or the like.

Application 7

According to another aspect of the invention, a method for manufacturingan optical element is provided. The method includes forming a pluralityof reflection layers on one side of a substrate such that the reflectionlayers are arranged in a striped manner in plan view, forming anabsorbing layer so as to cover the one side of the substrate and theplurality of reflection layers, and forming an oxide film by oxidizingportions of the absorbing layer on the side of the reflection layersopposite the substrate, in part, and portions of the absorbing layerbetween any two adjacent reflection layers.

In this method, the absorbing layer is formed after forming thereflection layers. This process can reduce variation in etching amountresulting from the difference in etching rate between the materialscompared to the case of forming the reflection layers and the absorbinglayer at one time by etching. Accordingly, finely striped reflectionlayers can be formed. Consequently, contrast and brightness can beimproved. Also, the oxide film formed between the reflection layersprevents decrease in optical transmittance between the reflectionlayers.

Application 8

Preferably, the method further includes forming grooves in the substratebetween any two adjacent reflection layers after the step of forming thereflection layers, and part of the oxide film is formed in the grooves.

In this method, the absorbing layer is formed after forming thereflection layers. This process can reduce variation in etching amountresulting from the difference in etching rate between the materialscompared to the case of forming the reflection layers and the absorbinglayer at one time by etching. Accordingly, finely striped reflectionlayers can be formed. Consequently, contrast and brightness can beimproved. Also, the oxide film is formed after the formation of thegrooves performed after the formation of the reflection layers byoxidizing the material (film) defining the grooves. Consequently, theportions between the reflection layers are nearly transparent, andaccordingly, the optical transmittance between the reflection layersdoes not decrease.

Application 9

According to still another aspect of the invention, a method formanufacturing an optical element is provided. The method includesforming a plurality of reflection layers on one side of a substrate suchthat the reflection layers are arranged in a striped manner in planview, forming an absorbing layer so as to cover the one side of thesubstrate and the plurality of reflection layers, and removing theportions of the absorbing layer between any two adjacent reflectionlayers by etching.

In this method, the substrate is exposed between the reflection layersby removing the portions of the absorbing layer between the reflectionlayers. Consequently, the optical transmittance between the reflectionlayers is increased.

Application 10

Preferably, the method further includes forming a dielectric layerbetween the reflection layers and the absorbing layers.

In this method, the dielectric layer between the reflection layers andthe absorbing layer prevents the constituent elements in the reflectionlayers and the absorbing layers from diffusing mutually. Thus,fluctuation in performance of separating polarized light components,resulting from diffusion can be reduced.

Application 11

Preferably, the reflection layers are formed of a material containing atleast one selected from the group consisting of aluminum, silver,copper, chromium, titanium, nickel, tungsten, and iron.

The reflection layers made of such a material allows an oxide film(dielectric layer) to be easily formed by thermal oxidation or the like.

Application 12

Preferably, the absorbing layer is formed of a material containing atleast one selected from the group consisting of silicon, germanium, andchromium.

The use of such a material achieves an optical element capable ofabsorbing light, that is, having a low reflectance.

Application 13

Preferably, the dielectric layer is formed of silicon oxide.

In this instance, the silicon oxide layer can be easily formed bythermal oxidation or the like.

Application 14

According to still another aspect of the invention, there is provided anelectronic apparatus including the above-described optical element.

The electronic apparatus includes the above-described optical elementcan exhibit improved display quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view of a polarization element.

FIG. 2 is a fragmentary sectional view of the polarization element takenalong a Y-Z plane.

FIG. 3 is a fragmentary sectional view of a polarization elementaccording to a first embodiment of the invention.

FIG. 4 is a flow diagram of a method for manufacturing a polarizationelement.

FIG. 5 is a schematic sectional view illustrating a specific step of themanufacturing method of the polarization element.

FIG. 6 is a schematic sectional view illustrating a specific step of themanufacturing method of the polarization element.

FIG. 7 is a schematic sectional view illustrating a specific step of themanufacturing method of the polarization element.

FIG. 8 is a schematic sectional view illustrating a specific step of themanufacturing method of the polarization element.

FIG. 9 is a schematic sectional view illustrating a specific step of themanufacturing method of the polarization element.

FIG. 10 is a schematic diagram of a projector incorporating anembodiment of the electronic apparatus according to the invention.

FIG. 11 is a plot illustrating the relationships between the pitch ofthe grid and brightness and between the pitch of the grid and contrastratio.

FIG. 12 is a plot illustrating the relationship between brightness andcontrast ratio.

FIG. 13 is a fragmentary sectional view of the polarization elementaccording to a second embodiment of the invention.

FIG. 14 is a flow diagram of a method for manufacturing a polarizationelement.

FIG. 15 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 16 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 17 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 18 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 19 is a flow diagram of a method for manufacturing a polarizationelement.

FIG. 20 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 21 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 22 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

FIG. 23 is a schematic sectional view illustrating a specific step ofthe manufacturing method of the polarization element.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some embodiments of the invention will be described below with referenceto the drawings. For the sake of visibility, the dimensional proportionsof the components or members in the drawings may be varied as needed.

First Embodiment

Polarization Element

The structure of the polarization element according to a firstembodiment will first be described with reference to FIGS. 1 to 3. FIG.1 is a schematic perspective view of a polarization element. FIG. 2 is afragmentary sectional view of the polarization element taken along a Y-Zplane. FIG. 3 is a fragmentary sectional view illustrating in detail apolarization element according to a first embodiment of the invention.

The drawings to which the following description refers are illustratedin an XYZ orthogonal coordinate system. The major parts of thepolarization element are described with reference to the XYZ rectangularcoordinate system. In the drawings, a plane parallel to the surface 11 cof a substrate 11 on which a grid is formed is defined as the X-Y plane.The grid is defined by ribs 12, or bar members, extending in the Xdirection and arranged in the Y direction.

As shown in FIGS. 1 and 2, a polarization element 1 includes a substrate11 and a grid defined by a plurality of ribs 12 arranged in a stripedmanner in plan view on the substrate 11. Each rib 12 of the gridincludes a reflective reflection layer 12 a, a dielectric layer 12 b onthe surface of the reflection layer 12 a, and an absorbing layer 12 c onthe top of the dielectric layer 12 b.

The substrate 11 is made of an optically transparent material, such asquartz or a plastic. The material is not particularly limited as long asit is optically transparent. In the present embodiment, the substrate 11is made of glass. In some applications, heat is stored in thepolarization element 1 and increases the temperature of the polarizationelement. Accordingly, a heat-resistant glass or quartz is advantageouslyused as the material of the substrate 11.

The reflection layer 12 a is defined by a long, thin metal memberextending in a direction on the substrate 11, and a plurality ofreflection layers are arranged on the substrate 11 parallel to eachother at a predetermined pitch. The reflection layer 12 a may be made ofa material having a high reflectance for visible light. Morespecifically, the material of the reflection layer 12 a may be aluminum,silver, copper, chromium, titanium, nickel, tungsten, or iron. In thepresent embodiment, the reflection layer 12 a is made of aluminum.

The dielectric layer 12 b is disposed so as to cover the surfaces of thereflection layers 12 a. The dielectric layer 12 b is made of a metaloxide, desirably a material having a high optical transmittance forvisible light, for example, a dielectric material such as aluminumoxide. The dielectric layer 12 b can be formed by oxidizing thereflection layer 12 a or by depositing a metal oxide layer, as will bedescribed later.

The dielectric layer 12 b acts as a barrier layer preventing theconstituent elements of the reflection layer 12 a and the absorbinglayer 12 c from mutually diffusing, and is optionally provided betweenthe reflection layer 12 a and the absorbing layer 12 c.

The dielectric layer 12 b may be made of any dielectric material as longas the material can form a barrier. For example, the dielectric layer 12b may be made of an oxide, a nitride or an oxynitride of silicon,aluminum, chromium, titanium, nickel, or tungsten.

The absorbing layer 12 c is disposed on the dielectric layer 12 bcovering the reflection layers 12 a and extends in the direction (Xdirection) in which the reflection layers 12 a extend. The absorbinglayer 12 c is made of a material having a higher optical absorptance forvisible light than the dielectric layer 12 b. More specifically, theabsorbing layer is made of at least one selected from the groupconsisting of silicon, germanium, and chromium. In the presentembodiment, the material of the absorbing layer 12 c is silicon.

Recessed portions 15 are formed, one each, between any two adjacent ribs12 of the grid. The recessed portions 15 are arranged in the Y directionat substantially regular intervals with a period shorter than thewavelengths of visible light. Each layer of a polarization element 1A(FIG. 3) of the present embodiment has the following dimensions.

The height of the reflection layer 12 a is, for example, about 180 nm.The width of the reflection layer 12 a is, for example, about 40 nm. Thethickness of the dielectric layer 12 b on the reflection layer 12 a is,for example, about 10 nm to 20 nm. The thickness of the absorbing layer12 c is, for example, 10 nm to 20 nm.

The interval, or space S, between any two adjacent ribs 12 of the gridis, for example, about 70 nm. The period, or pitch P, of the ribs 12 is,for example, 140 nm.

Since the ribs 12 of the grid have a multilayer structure including thereflection layer 12 a, the dielectric layer 12 b, and the absorbinglayer 12 c, the ribs 12 of the grid can transmit transverse-magnetic(TM) waves 21 that are polarized light (linearly polarized light)oscillating in a direction (Y direction) perpendicular to the directionin which the ribs 12 extend, and can absorb transverse-electric (TE)waves 22 that are polarized light (linearly polarized light) oscillatingin the direction (X direction) in which the ribs 12 extend.

More specifically, the TE waves 22 that have entered the grid throughthe absorbing layer 12 c are damped mainly by light absorption of theabsorbing layer 12 c and may also be damped by the dielectric layer 12 bin some cases. The portion of the TE waves 22 that has passed throughthe dielectric layer 12 b is reflected at the reflection layer 12 a(acting as a part of a wire grid).

The reflected TE waves 22 pass through the dielectric layer 12 b. Atthis time, the TE waves have a phase difference and are damped byinterference and absorbed by the absorbing layer 12 c. Thus, the gridhas the effect of damping TE waves 22. Accordingly, the polarizationelement can separate polarized light components as desired byabsorption. The transmittance of the grid for TE waves 22 may be, forexample, 1% or less.

On the other hand, TM waves 21 are transmitted with a high transmittanceof, for example, 80% or more. The contrast ratio defined by TM/TE isdesirably 1000 or more.

As shown in FIG. 3, the polarization element 1A of the first embodimenthas grooves 16 in the substrate 11 between any two adjacent ribs 12 ofthe grid. In each groove 16, an oxide film 12 b 1 or 12 c 1 of, forexample, silicon oxide, is formed when the dielectric layer 12 b or theabsorbing layer 12 c is formed.

In the present embodiment, the grooves 16 are formed in the substrate 11between the ribs 12 of the grid, and some film in the grooves isoxidized into an oxide film. Therefore, the portions between the ribs 12are nearly transparent, and accordingly the optical transmittance ofthose portions does not decrease.

Method for Manufacturing Polarization Element

A method for manufacturing the polarization element 1A of the firstembodiment will now be described with reference to FIGS. 4 to 9. FIG. 4is a flow diagram of the manufacturing method of the polarizationelement. FIGS. 5 to 9 are schematic sectional views each illustrating aspecific step of the manufacturing method.

As shown in FIG. 4, the method for manufacturing the polarizationelement 1A of the first embodiment includes step S11 of formingreflection layers, step S12 of forming grooves, step S13 of forming adielectric layer, step S14 of forming an absorbing layer, and step S15of heat treatment.

First, reflection layers 12 a are formed as shown in FIG. 4 in Step S11.More specifically, first, aluminum is deposited on the substrate 11 by aknown method. Subsequently, a resist pattern is formed by a two-beaminterference exposure method, and the deposited aluminum film ispatterned into wire grid reflection layers 12 a by using the resistpattern as a mask. Thus, the reflection layers 12 a are formed in astriped manner on the substrate 11, as shown in FIG. 5.

Then, in Step S12, grooves 16 are formed, as shown in FIG. 6. Morespecifically, the grooves 16 are formed in the substrate 11 between anytwo adjacent reflection layers 12 a. This operation for forming thegrooves 16 may be performed by, for example, dry etching of thesubstrate 11. The depth of the grooves 16 is preferably at least suchthat the oxide films 12 b 1 and 12 c 1, which will be formed later byoxidizing the dielectric layer 12 b and the absorbing layer 12 c, liewithin the grooves below the height of the grooves.

In Step S13, a dielectric layer 12 b is formed. More specifically, thedielectric layer 12 b is formed as shown in FIG. 7 by, for example,heating the substrate 11 to oxidize the surfaces of the reflectionlayers 12 a. For this operation for heating the substrate 11, forexample, atmospheric-pressure annealing may be performed in a heatingfurnace. The temperature for heating the substrate 11 may be 300° C.

The thickness of the dielectric layer 12 b is about 10 nm to 20 nm asmentioned above. Thus, a dielectric layer 12 b of aluminum oxide (AlOx)is formed over the surfaces of the reflection layers 12 a.

In Step S14, an absorbing layer 12 c is formed. More specifically, theabsorbing layer 12 c is formed of silicon or the like on the dielectriclayer 12 b, as shown in FIG. 8, by a known magnetron sputtering methodor the like. The thickness of the absorbing layer 12 c is 10 nm to 20 nmas mentioned above.

In Step S15, thermal oxidation is performed. More specifically, thesubstrate 11 is subjected to heat treatment so as to thermally oxidizethe silicon remaining on the surface of the substrate 11 between theribs 12 of the grid into silicon oxide (SiO₂), as shown in FIG. 9. Thus,the silicon film between the ribs 12 can be oxidized through thisoperation although the surface of the absorbing layer 12 b is partiallyoxidized into an oxide film 12 c 1.

In this manufacturing method, the film between the ribs of the ribs 12is oxidized into oxide film 12 c 1. Thus, the resulting film is nearlytransparent, and accordingly the optical transmittance of the grid doesnot decrease between the ribs 12. The polarization element 1A is thuscompleted.

Electronic Apparatus

An electronic apparatus according to an embodiment of the invention willnow be described with reference to FIG. 10. FIG. 10 is a schematicdiagram of a projector incorporating an embodiment of the electronicapparatus.

As shown in FIG. 10, the projector 800 includes a light source 810,dichroic mirrors 813 and 814, reflection mirrors 815, 816, and 817, anentrance lens 818, a relay lens 819, an emission lens 820, opticalmodulators 822, 823, and 824, a cross dichroic prism 825, and aprojection lens 826.

The light source 810 includes a lamp 811, such as a metal halide lamp,and a reflector 812 capable of reflecting the light emitted from thelamp. The light source 810 may be an ultrahigh-pressure mercury-vaporlamp, a mercury flash lamp, a high-pressure mercury-vapor lamp, a deepUV lamp, a xenon lamp, a xenon flash lamp, or the like, instead of themetal halide lamp.

The dichroic mirror 813 transmits the red component of white lightemitted from the light source 810 and reflects the blue and greencomponents of the white light. The red component transmitted through thedichroic mirror is reflected to the optical modulator 822 of red lightfrom the reflection mirror 817. The green component of the blue andgreen components reflected from the dichroic mirror 813 is reflected tothe optical modulator 823 of green light from the dichroic mirror 814.The blue component is transmitted through the dichroic mirror 814 andenters the optical modulator 824 of blue light through an optical relaysystem 821 adapted to prevent light from being lost through a longoptical path and including the entrance lens 818, the relay lens 819,and the emission lens 820.

Each of the optical modulators 822, 823, and 824 includes polarizationelements 840 and 850 with a liquid crystal light valve 830 therebetween.The above-described polarization element 1 (1A) is used as thepolarization elements 840 and 850. The polarization element 840 isdisposed on the optical path of the light emitted from the light source810, between the light source 810 and the liquid crystal light valve830. The polarization element 850 is disposed on the optical path of thelight that has passed through the liquid crystal light valve 830,between the liquid crystal light valve 830 and the projection lens 826.The transmission axes of the polarization elements 840 and 850 areperpendicular to each other; hence the polarization elements are in across-Nicol arrangement.

The polarization elements 840 and 850 used in the projector 800 of thepresent embodiment are made of a heat-resistant inorganic material, andthe deterioration of the polarization elements 840 and 850 issuppressed.

The three color light components modulated by the respective opticalmodulators 822, 823, and 824 enter the cross dichroic prism 825. Thecross dichroic prism 825 is composed of four right-angle prisms bondedtogether, and a dielectric multilayer film capable of reflecting the redlight component and a dielectric multilayer film capable of reflectingthe blue light component are formed in an X-shaped manner at theinterfaces of the four prisms. The three color light components aresynthesized into a light forming a color image by the dielectricmultilayer films. The synthesized light is projected on a screen 827through the projection lens 826, or projection optical system, thusforming an enlarged image.

The projector 800 that is a type of electronic apparatus includes thepolarization element 1 of the above-described embodiment and, therefore,can exhibit good reliable performance to display images.

The electronic apparatus including the above-described polarizationelement 1 can be embodied as any one of a variety of apparatuses, suchas head-mounted displays (HMD), head-up displays (HUD), smartphones,electrical view finders (EVF), cellular phones, mobile computers,digital cameras, digital video cameras, automotive equipment, andlighting devices, in addition to the projector 800.

Optical Properties

The optical properties of the polarization element according to thepresent embodiment will be described below with reference to FIGS. 11and 12. FIG. 11 is a plot illustrating the relationships between thepitch of the grid (WG) and brightness and between the pitch of the gridand contrast. FIG. 12 is a plot illustrating the relationship betweenbrightness and contrast.

The measurements of brightness and contrast were performed under theassumption that the polarization element would be used as thepolarization element of a light valve in the above-described projector800. The polarization element 1 according to an embodiment of theinvention is made of inorganic materials and is highly resistant toheat. Accordingly, the polarization element can be used as a polarizerof the above-described projector 800 including a high-power lightsource.

In the plot shown in FIG. 11, the horizontal axis represents the pitch(nm) of the grid ribs 12, which was varied from 50 nm to 150 nm. Thevertical axis on the left side represents brightness Tp (%) in the rangeof 90% to 98%. The vertical axis on the right side represents contrastratio in the range of 0 to 12000.

As shown in FIG. 11, brightness increases as the pitch of the grid ribs12 is reduced. This relationship is however reversed at a pitch of about80 nm, and brightness decreases as the pitch is reduced.

Similarly, contrast ratio increases as the pitch is reduced. It isdifficult to determine the peak value of the contrast ratio within therange shown in FIG. 11. This plot suggests that the pitch of the gridribs 12 relates greatly to brightness and contrast.

In the plot shown in FIG. 12, the horizontal axis represents brightnessTp (%) in the range of 90% to 98%. The vertical axis represents contrastratio in the range of 0 to 12000.

As shown in FIG. 12, brightness reaches the peak value of 96% at acontrast ratio of about 4000. When the contrast ratio is increased to12000 from 4000, however, the brightness decreases.

Desirably, the pitch of the grid ribs 12 is set according to theprocessing precision, usage environment and purpose of the grid.

The first embodiment including the polarization element 1A, themanufacturing method of the polarization element 1A, and the electronicapparatus produces the following effects.

(1) According to the polarization element 1A of the first embodiment andthe method for manufacturing the polarization element, the dielectriclayer 12 b and the absorbing layer 12 c are formed after the reflectionlayers 12 a have been formed. This process can reduce variation inetching amount resulting from the difference in etching rate betweenmaterials compared to the case of forming the reflection layers 12 a,the dielectric layer 12 b, and the absorbing layer 12 c at one time byetching a multilayer composite including these layers. Thus, the gridribs 12, each including the striped reflection layer 12 a, thedielectric layer 12 b, and the absorbing layer 12 c can be regularlyarranged. Consequently, contrast and brightness are improved. Also, thefilms between the grid ribs 12 are oxidized into oxide films 12 b 1 and12 c 1. Consequently, the optical transmittance of the grid does notdecrease between the ribs.

(2) According to the polarization element 1A of the first embodiment andthe method for manufacturing the polarization element 1A, grooves 16 areformed in the substrate 11 between the grid ribs 12, and a film in thegrooves 16 is oxidized into an oxide film 12 c 1. The portions betweenthe grid ribs 12 are therefore nearly transparent. The decrease inoptical transmittance between the grid ribs 12 is thus prevented.

(3) In the manufacturing method of the first embodiment, thepolarization element 1A can be produced by using a conventionaltechnique, such as a vacuum process, sputtering, or photolithography.The method of the first embodiment increases productivity. In addition,manufacturing cost can be reduced.

(4) The projector 800 of the first embodiment, which includes thepolarization element 1A of the first embodiment, can be an electronicapparatus that can exhibit improved display quality.

Second Embodiment

Polarization Element

The structure of the optical element according to a second embodimentwill now be described with reference to FIG. 13. FIG. 13 is afragmentary sectional view of a polarization element according to thesecond embodiment of the invention.

The polarization element 1B of the second embodiment is different fromthe polarization element 1A of the first embodiment in that grooves 16are not formed in the substrate 11. Except for this difference, thestructures of these two polarization elements are substantially thesame. In the second embodiment, therefore, different points from thefirst embodiment will be described, and other points are omitted.

As shown in FIG. 13, the polarization element 1B includes a substrate 11and a grid defined by a plurality of ribs arranged in a striped mannerin plan view on the substrate 11 and is thus similar to the polarizationelement 1A of the first embodiment. Each rib 12 of the grid includes areflection layer 12 a, a dielectric layer 12 b on the surface of thereflection layer 12 a, and an absorbing layer 12 c on the top of thedielectric layer 12 b.

Unlike the first embodiment, grooves 16 are not formed between any twoadjacent grid ribs 12. The portions of the substrate between the gridribs 12 are each provided thereon with an oxide film 12 c 1 of, forexample, silicon oxide formed by forming the dielectric layer 12 b andthe absorbing layer 12 c.

Method for Manufacturing Polarization Element

A method for manufacturing the polarization element 1B of the secondembodiment will now be described with reference to FIGS. 14 to 18. FIG.14 is a flow diagram of the manufacturing method of the polarizationelement. FIGS. 15 to 18 are schematic sectional views each illustratinga specific step of the manufacturing method.

As shown in FIG. 14, the method for manufacturing the polarizationelement 1B of the second embodiment includes step S21 of formingreflection layers, step S22 of forming a dielectric layer, step S23 offorming an absorbing layer, and step S24 of heat treatment.

In Step S21, reflection layers 12 a are formed as shown in FIG. 15. Morespecifically, wire grid reflection layers 12 a are formed of aluminum orthe like by a two-beam interference exposure method, as in the firstembodiment.

In Step S22, a dielectric layer 12 b is formed. More specifically, thedielectric layer 12 b is formed by, for example, heating the substrate11 to oxidize the surfaces of the reflection layers 12 a, as shown inFIG. 16. The heating is performed in the same manner as in the firstembodiment. Thus, a dielectric layer 12 b of aluminum oxide (AlOx) isformed over the surfaces of the reflection layers 12 a.

In Step S23, an absorbing layer 12 c is formed. More specifically, theabsorbing layer 12 c is formed of silicon or the like on the dielectriclayer 12 b, as shown in FIG. 17, by a known magnetron sputtering methodor the like.

In Step S24, thermal oxidation is performed. More specifically, thesubstrate 11 is subjected to heat treatment so as to oxidize the siliconremaining on the surface of the substrate 11 between the ribs 12 of thegrid into silicon oxide (SiO₂), as shown in FIG. 18. Polarizationelement 1B is thus completed.

The second embodiment including the polarization element 1B and themanufacturing method thereof produces the following effects.

(5) In the polarization element 1B of the second embodiment, oxide films12 c 1 and 12 b 1 are formed without forming grooves 16 between the ribsof the grid 12. The number of steps in the manufacturing process isreduced, and accordingly the cost in manufacture can be reduced.

Third Embodiment

Method for Manufacturing Polarization Element

A method for manufacturing the polarization element 1C of the thirdembodiment will now be described with reference to FIGS. 19 to 23. FIG.19 is a flow diagram of the manufacturing method of the polarizationelement. FIGS. 20 to 23 are schematic sectional views each illustratinga specific step of the manufacturing method.

The polarization element 1C of the third embodiment has the samestructure as the polarization element 1 shown in FIG. 1. Polarizationelement 1C is formed by substantially the same manufacturing method asin the second embodiment, except that etching is performed instead ofthermal oxidation. In the third embodiment, therefore, different points(manufacturing method) from the second embodiment will be described, andother points are omitted.

As shown in FIG. 19, the method for manufacturing the polarizationelement 1C of the third embodiment includes step S31 of formingreflection layers, step S32 of forming a dielectric layer, step S33 offorming an absorbing layer, and step S34 of etching.

Steps S31 to S33 (FIGS. 20 to 22) are the same as Steps S21 to S23(FIGS. 15 to 17) in the second embodiment. However, Step S32 of forminga dielectric layer 12 b may be performed by sputtering.

In Step S34, etching is performed. More specifically, the residue (oxidefilm 12 b 1 and absorbing layer 12 c) on the substrate 11 between theribs 12 of the grid is removed by etching, as shown in FIG. 23. For thisetching, for example, Cl₂ gas or CF₄ gas is used. Thus, the surface ofthe substrate is exposed between the ribs 12 of the grid, andpolarization element 1C is completed.

The third embodiment including the polarization element 1C and themanufacturing method thereof produces the following effects in additionto the effects of the first and the second embodiment.

(6) In the polarization element 1C of the third embodiment, the film onthe substrate 11 between the ribs 12 of the grid is moved. Accordingly,the optical transmittance is increased compared to the case where oxidefilm lies between the ribs 12 of the grid.

The invention is not limited to the disclosed embodiments, and variousmodifications may be made within the scope and spirit of the inventionas set forth in or understood from the appended claims and thedescription of the Specification. The embodiments may be modified asbelow.

Modification 1

The grid may be made up of, for example, reflection layers 12 a and anabsorbing layer 12 c without being limited to the structure includingreflection layers 12 a, a dielectric layer 12 b, and an absorbing layer12 c.

Modification 2

The oxide film between the grid ribs 12 are not always formed by thermaloxidation and may be formed by using any other technique such aschemical reaction.

This application claims priority to Japan Patent Application No.2015-157969 filed Aug. 10, 2015, the entire disclosure of which ishereby incorporated by reference in its entirety.

What is claimed is:
 1. A method for manufacturing an optical element,the method comprising: forming a plurality of reflection layers on oneside of a substrate such that the reflection layers included in theplurality of reflection layers are arranged in a striped manner in aplan view; forming, subsequent to the forming of the plurality ofreflection layers arranged in the striped manner, an absorbing layer soas to cover the one side of the substrate and the plurality ofreflection layers; and forming an oxide film by oxidizing portions ofthe absorbing layer on a side of the plurality of reflection layersopposite the substrate, in part, and portions of the absorbing layerbetween any two adjacent reflection layers included in the plurality ofreflection layers.
 2. The method according to claim 1, furthercomprising forming grooves in the substrate between the any two adjacentreflection layers included in the plurality of reflection layers afterthe step of forming the plurality of reflection layers, wherein part ofthe oxide film is formed in the grooves.
 3. The method according toclaim 1, further comprising forming a dielectric layer between theplurality of reflection layers and the absorbing layer.
 4. The methodaccording to claim 3, wherein the dielectric layer is formed of siliconoxide.
 5. The method according to claim 1, wherein the reflection layersincluded in the plurality of reflection layers are formed of a materialcontaining at least one selected from the group consisting of aluminum,silver, copper, chromium, titanium, nickel, tungsten, and iron.
 6. Themethod according to claim 1, wherein the absorbing layer is formed of amaterial containing at least one selected from the group consisting ofsilicon, germanium, and chromium.
 7. A method for manufacturing anoptical element, the method comprising: forming a plurality ofreflection layers on one side of a substrate such that the reflectionlayers included in the plurality of reflection layers are arranged in astriped manner in a plan view; forming, subsequent to the forming of theplurality of reflection layers arranged in the striped manner, anabsorbing layer so as to cover the one side of the substrate and theplurality of reflection layers; and removing portions of the absorbinglayer between any two adjacent reflection layers included in theplurality of reflection layers by etching.
 8. The method according toclaim 7, further comprising forming a dielectric layer between theplurality of reflection layers and the absorbing layer.
 9. The methodaccording to claim 8, wherein the dielectric layer is formed of siliconoxide.
 10. The method according to claim 7, wherein the reflectionlayers included in the plurality of reflection layers are formed of amaterial containing at least one selected from the group consisting ofaluminum, silver, copper, chromium, titanium, nickel, tungsten, andiron.
 11. The method according to claim 7, wherein the absorbing layeris formed of a material containing at least one selected from the groupconsisting of silicon, germanium, and chromium.